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Date: Wed, 4 Feb 2009 08:00:05 -0800
From: Andrew Thompson <thompsa@FreeBSD.org>
To: Hans Petter Selasky <hselasky@c2i.net>
Message-ID: <20090204160005.GB77595@citylink.fud.org.nz>
References: <200902041242.n14CgXj2014958@repoman.freebsd.org>
	<200902041459.35445.hselasky@c2i.net>
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Cc: Perforce Change Reviews <perforce@freebsd.org>,
	Weongyo Jeong <weongyo@freebsd.org>
Subject: Re: PERFORCE change 157132 for review
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On Wed, Feb 04, 2009 at 02:59:35PM +0100, Hans Petter Selasky wrote:
> On Wednesday 04 February 2009, Weongyo Jeong wrote:
> > ????????bzero(desc, sizeof(struct uath_tx_desc));
> > ????????desc->msglen = htobe32(sizeof(struct uath_tx_desc));
> > -???????desc->msgid ?= data_idx + 1;????/* don't care about endianness */
> > +???????desc->msgid ?= (sc->sc_msgid++) + 1;????/* don't care about
> > endianness */ desc->type ? = htobe32(WDCMSG_FLUSH);
> > ????????desc->txqid ?= htobe32(0);
> > ????????desc->connid = htobe32(0);
> 
> Why not allocate an mbuf to hold the "descriptor" data. Then you use the 
> m_next field of the header mbuf to link with the "data" mbuf ? Then you only 
> need one [mbuf] queue for TX ? You can look at if_ural2.c and if_rum2.c 
> in /sys/dev/usb2/wlan .

Because uath_data+uath_tx_desc is preallocated so you do not have to
malloc in the TX path. Grabbing a mbuf could fail due to low memory.


Andrew